Traditionally, flatproof tires have been made by one of the following methods. In one method, a solid polyurethane material is injected into a solid mold for producing a flatproof tire. The mold with the solid polyurethane material is heated and rotated, and then allowed to cure. After curing the solid polyurethane tire is removed from the mold.
Another flatproofing method offered by several companies including, Arnco, CinAir and Carpenter, is generally known as “traditional fill” and involves filling a rubber tire mounted on a wheel with solid polyurethane. Polyurethane reactants (a polyol and an isocyanate) are mixed using a static mixer and pumped into the tire through the valve stem in the wheel under the same pressure as the normal air inflation pressure for the tire. The reactant mixture is then allowed to cure inside the tire forming a solid polyurethane fill within the tire. Typically, an extender, such as an oil, is included in the reactant mixture. Solid polyurethane, however, is very heavy. For example, a typical solid polyurethane fill with an oil extender has no cells and has a high density of about 62.4 lbs/ft3 making it practical for use only with heavy equipment. This method has additional drawbacks. Because the reactants are pumped into the tire under pressure, namely the normal inflation pressure of the tire, the tire must be filled while placed within a safety cage in case the tire fails during filling.
Other flatproofing methods use non-urethane flatproofing materials that do not replace the air in the tire and wheel assembly. They seal leaks and/or punctures in the tire to minimize the loss of air. In this regard, these non-urethane flatproofing materials are not considered flatproof.
From the above, it can be appreciated that it would be desirable to have a flexible, lightweight polyurethane foam that replaces the inflating air in the tire as a means to support the tubeless rubber tire allowing it to be used in low speed applications and applications other than for heavy equipment. Examples of such desired low speed, light weight applications include, off-road, construction and turf and garden applications. Such flexible foam would provide the pneumatic performance of an air inflated pneumatic tire due to its flexible cell walls, semi-open cell structure, and density, size and uniform distribution of the cells. It can also be appreciated that it would be desirable to have a process for flatproofing a tire and wheel assembly by injecting liquid reactant materials into the tire and wheel assembly to form a flexible polyurethane foam that replaces the inflating air in the tubeless tire and wheel assembly that is relatively maintenance free. Further, it can be appreciated that it would be desirable to have a portable apparatus that injects the liquid reactant materials into a tubeless tire and wheel assembly for flatproofing, and can be used in the field by the tire dealers, avoiding the need to return the tire to a factory. Further it can be appreciated that it would be desirable for safety considerations to have a fill process that does not require the tire cavity to be pressurized.